1. Field of the Invention
The present invention relates to a fuel supply system for supplying fuel to an internal combustion engine, and more specifically, to a device for distributing the fuel to a plurality of engine cylinders.
2. Description of the Prior Art
In automotive vehicle engines or other power engines, fuel injection systems for supplying pressurized fuel in an injected manner have been widely used. In the fuel injection systems of this type, in general, pressurized fuel in a delivery pipe having a given volume is distributed to a plurality of fuel injection valves and then injected into an intake passage of each engine cylinder or into a combustion chamber of each cylinder. Such fuel injection systems have been applied to gasoline engines and diesel engines. In general, in these fuel injection systems, a pressure regulator is provided for adjusting a fuel pressure in the delivery pipe to a given value. Specifically, when the fuel pressure in the delivery pipe exceeds the given value, the pressure regulator is opened to return an excess portion of the fuel to a fuel tank.
However, the excess fuel returned to the fuel tank from the delivery pipe provided near the engine is in general, increased in temperature due to heat of the engine so that it tends to generate fuel vapor. Further, since the excess fuel is subjected to a pressure reduction from a high-pressure state in the delivery pipe to a low-pressure state in the fuel tank, it further tends to generate the fuel vapor.
Further, in the foregoing fuel injection systems, in order to prevent the fuel vapor from being discharged from the fuel tank into the atmosphere, a canister is required for collecting the fuel vapor, which leads to complexity in structure and increment in cost of the whole system.
On the other hand, it has been proposed to omit the pressure regulator and prohibit the return of the excess fuel to the fuel tank so as to suppress generation of the fuel vapor.
However, when return of the excess fuel is prohibited, bubbles of air enter the delivery pipe or bubbles of the fuel vapor generated in the delivery pipe remain in the delivery pipe. These gas components reduce a supply amount of the fuel as liquid so as to impede an stable operation of the engine and deteriorate exhaust gas emissions.